1. Field of the Invention
The present invention relates to a control device for a watercraft propulsion system that can control a watercraft to move automatically at an extremely slow speed when it is necessary.
2. Description of the Related Art
In a so-called trolling manner, in which a watercraft is not anchored, it is a very important challenge for a watercraft operator to operate the watercraft so as not to drift but to position an end of a fishing line at a “point” where fish flock (hereunder, called merely “point”). The operator making use of the trolling manner performs a particular navigation to continuously locate the end of the fishing line at the “point”. The navigation is performed to slightly move the watercraft forward or backward while alternating a state in which a forward gear or a reverse gear is in an engaging position and a state in which both of the forward and reverse gears are disengaging positions in a short period and repeating the alternations. In this description, the navigation will be referred to as “extremely slow speed navigation.” Conventionally, the extremely slow speed navigation is made by a watercraft operator who repeatedly changes a remote controller shift lever, which is located at a cockpit, between a forward position (or a reverse position) and a neutral position at short intervals generally existing in a range of several seconds through tens of seconds.
However, in the conventional extremely slow speed navigation state, the watercraft operator needs to perform change operations of the remote controller shift lever while foreseeing and determining the fact that the watercraft does not stop due to inertia and other circumstances by making use of his or her experiences and imaginations (intuitions). Therefore, every watercraft operator may have his or her own frequencies for the change operations of the remote controller shift lever per unit time. Particularly, watercraft operators who have less experience are likely to have a number of frequencies for the change operations of the remote controller shift lever. Accordingly, there have been indications that a life of a shift mechanism for a watercraft propulsion system (engine) can be extremely short and other drawbacks can happen because clutch change times increase and a clutch is burdened.
On the other hand, in the trolling manner, it is of course quite desirable that the watercraft stays at the point for a longer period of time, regardless of broadness or narrowness of the “point”, to locate the maximum number of fish. If, however, the “point” has a broad area, the watercraft operator needs to fish while moving the watercraft over a long distance. The watercraft operator thus is required to move the watercraft back to a point or the like where the watercraft started to drift as soon as possible in order to perform effective fishing with ample time that can be almost entirely dedicated to the fishing.
On the other hand, if the so-called hands-free watercraft navigation (automatic watercraft navigation) is practicable for a longer period of time, the operation is convenient for the watercraft operator because the watercraft operator may spend much time for confirming the safety of passengers and the watercraft, and performing other operations. However, the watercraft operator needs to perform change operations of the shift lever in the conventional speed navigation state. Accordingly, there arises a problem that the hands-free operation is difficult in the extremely slow speed navigation state more than in a navigation state in which the watercraft is moved forward or backward while the forward gear or the reverse gear is engaged (in the description, this navigation is referred to as “normal navigation”).
In the meantime, the following outboard motor is known as the watercraft propulsion system. As disclosed in JP-A-2006-021557, the outboard motor has a structure which performs a single shift control whereby an electric motor for a shift operation is controlled so that a shift position is periodically changed between a forward or reverse (gear-in) position and a neutral position. Skill for the watercraft navigation thus can vary more or less according to each watercraft operator. That is, differences inevitably exist between watercraft navigation skills of individual watercraft operators. In other words, the outboard motor noted above has a limit in the minute shift control (watercraft navigation) that is adapted to the trolling operation. Therefore, the outboard motor is far from sufficient for resolving the problems described above and still gives rise to problems such that the watercraft operator cannot easily make much time for other operations.